1. Field of the Invention
The present invention relates to battery testers and methods for testing batteries, and more particularly relates to testers useful for testing automotive batteries and methods useful for testing automotive batteries.
2. Description of the Related Art
Current methods for determining the condition of lead acid batteries (automotive batteries) are based upon the measurement of the internal resistance or dynamic conductance of the battery. Internal resistance or dynamic conductance value as compared to the size and state of the charge of the battery under test to determine its condition. The conventional direct current methods have typically involved measuring the internal resistance of the battery based on Ohm's law. The internal resistance of the battery is calculated by R.sub.i =V.sub.ocv -V.sub.load/ I.sub.load. It has been found that internal resistance of the battery measured by a direct current method varies with the current (I.sub.load). Internal resistance of the battery is higher as the current is made smaller. Conventional methods used to measure the internal resistance of the battery have typically used very high direct current for example 50 amps or more. Using very high direct current minimizes the effect of changes in internal resistance due to change in the test current. While the high direct current method has proven to have certain advantages, it has also exhibited certain disadvantages, including typically requiring very bulky and expensive test equipment, requiring that the battery have enough charge in order to perform the test, and requiring the use of very high currents which change the condition of the battery temporarily so that test results are not repeatable. Consequently, there is a desire to provide test methods and equipment which overcome these disadvantages.
Other methods used for determining the condition of lead acid batteries have involved measuring the dynamic conductance/resistance of the battery by charging the battery by a time varying voltage making periodic step transitions at a pre-determined frequency between two discreet levels or exciting the battery by a time varying discharge current making periodic transitions between levels at a pre-determined frequency. Corresponding periodic change in battery terminal voltage is monitored to calculate the battery dynamic conductance/resistance. Battery terminal voltages change periodically and can be separated from the battery direct current voltage and amplified for measurement, thereby allowing the use of very small charge or discharge current and the apparatus required for making the internal resistance measurement typically requires a lesser amount of hardware than the very high direct current method. Thus, the above method allows for determining the condition of the battery and the utilization of hand held testers. However, such conventional dynamic methods involve various disadvantages. These disadvantages include relying on the open circuit voltage to determine the state of charge of the battery which can be very misleading due to several reasons including (a) the presence of surface charge which can greatly affect the open circuit voltage, (b) the battery was under charge or discharge conditions and was not allowed to stabilize for sufficient time, thereby permitting the open circuit voltage reading to be very misleading for judging the state of charge, and (c) variations in the design and construction of the battery can have a great influence on the open circuit voltage which in turn may not be a very good indicator of the state of charge of the battery for the wide population of automotive batteries designed for different applications. Additional problems with dynamic tests include that dynamic conductance/resistance varies significantly with the state of charge, and specifically provides difficulties associated with the measurement of exact state of charge in a deep discharge state, and more specifically cannot effectively diagnosis batteries which are deeply discharged.
Both of the above conventional methods are widely used, however they have exhibited great difficulty in diagnosing battery conditions when the batteries are deeply discharged since both methods depend upon the internal resistance or dynamic conductance/resistance measurement, which changes with the state of charge of the battery. When the battery is completely discharged or deeply discharged, it is very difficult to assess its state of charge by the above methods.
Consequently, there is a need and a desire to provide a device which can be in a light weight, handheld form, and which can provide an accurate diagnosis of batteries in very discharged state.
Various prior electronic battery testing devices and methods are set out as follows:
Klingbiel U.S. Pat. No. 5,592,093 issued Jan. 7, 1997 which discloses an electronic battery testing device which utilizes a bridge circuit and amplified output to indicate presence of a loose connection; Champlin U.S. Pat. No. 5,140,629 issued Aug. 18, 1992 which discloses an electronic tester involving a dynamic conductance method; Champlin U.S. Pat. No. 4,825,170 issued Apr. 25, 1989 which discloses an electronic battery testing device which utilizes a dynamic conductance measurement method; Champlin U.S. Pat. No. 5,598,098 issued Jan. 28, 1997 which discloses an electronic battery tester which uses a dynamic conductance measurements involving; Champlin U.S. Pat. No. 5,572,136 issued Nov. 5, 1996 which discloses an electronic battery testing device which utilizes a time varying current signal measuring internal resistance; Champlin U.S. Pat. No. 4,816,768 issued Mar. 28, 1989 which discloses utilization of an electronic battery testing device for measuring dynamic conductance; Harper, et al. U.S. Pat. No. 5,438,270 issued Aug. 1, 1995 which discloses a battery tester comparing load and no load battery voltage utilizing a potential divider coupled to the battery; McShane, et al. U.S. Pat. No. 5,574,355 issued Nov. 12, 1996 which discloses a method and apparatus for detection and control of thermal runaway in battery undercharged involving determining internal resistance or conductance of the battery undercharge; Champlin U.S. Pat. No. 5,585,728 issued Dec. 17, 1996 which discloses an electronic tester with compensation for low state of charge for measuring dynamic conductance; Champlin U.S. Pat. No. 3,909,708 issued Sep. 30, 1975 which discloses an electronic battery testing device for making dynamic measurements; Champlin U.S. Pat. No. 3,873,911 issued Mar. 25, 1975 which utilizes an oscillator in the measurement of dynamic resistance; Windebank U.S. Pat. No. 4,433,294 issued Feb. 21, 1984 which discloses a method and apparatus for testing a battery by obtaining the dynamic voltage-current characteristic of the battery; Poljack U.S. Pat. No. 4,659,994 issued Apr. 21, 1987 which discloses a battery tester having first and second flip-flop means for testing lithium sulfur dioxide batteries; Windebank U.S. Pat. No. 4,396,880 issued Aug. 2, 1993 which discloses a method and apparatus for charging a battery involving evaluating the dynamic voltage/current characteristic of the battery; De La rosa U.S. Pat. No. 5,519,383 which discloses a battery and starter circuit monitoring system; Champlin U.S. Pat. No. 4,881,038 issued Nov. 14, 1989 which discloses an electronic battery device with automatic voltage scaling to determine dynamic conductance; Ritter U.S. Pat. No. 3,889,248 issued Jun. 10, 1975 which discloses a faulty battery connection indicator; Seyl U.S. Pat. No. 3,607,673 which discloses a method for measuring corrosion rates in a battery; Champlin U.S. Pat. No. 4,816,768 issued Mar. 28, 1989 which discloses an electronic battery testing device for measuring dynamic conductance; Champlin U.S. Pat. No. 4,912,416 issued Mar. 27, 1990 which discloses an electronic battery testing device with state of charge compensation; Abert U.S. Pat. No. 4,080,560 which discloses a method and apparatus for determining the maintenance and charge condition of lead acid storage batteries utilizing a heavy current load; Theron, et al. U.S. Pat. No. 4,290,021 issued Sep. 15, 1981 which discloses a battery testing method and device; Reni, et al. U.S. Pat. No. 5,352,968 issued Oct. 4, 1994 which discloses a method and apparatus for determining the charged state of a battery; Furuishi, et al. U.S. Pat. No. 3,753,094 issued Aug. 14, 1973 which discloses a method and device for measuring the internal resistance of a battery; Frailing, et al. U.S. Pat. No. 4,193,025 which discloses an automatic battery analyzer; Ottone U.S. Pat. No. 4,352,067 which discloses a battery analyzer utilizing a load bank to maintain a plurality of resisters in selective parallel interconnection; Marion, et al. U.S. Pat. No. 4,423,378 issued Dec. 27, 1983 which involves automotive battery test apparatus testing dynamic internal resistance of a battery; Alber, et al. U.S. Pat. No. 4,707,795 which discloses battery testing and monitoring system for continuously monitoring a battery voltage; McShane, et al. U.S. Pat. No. 5,574,355 issued Nov. 12, 1996 which discloses a method and apparatus for detection and control of thermal runaway in a battery under charge, all of which are incorporated herein by reference. As set out above, these prior methods and devices suffer from one or more problems which are overcome by the present method and device.